Brake system, generator and wind turbine

ABSTRACT

A brake system, especially for a generator, including a rotor assembly, a stator assembly and a rotation axis is disclosed. The rotor assembly includes an outer portion which is located radially outward of the stator assembly. The outer portion includes a brake disc, and the stator assembly comprises at least one frictional member operatively configured for frictionally engaging at least a portion of the brake disc.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority of European Patent Office applicationNo. 09014766.1 EP filed Nov. 26, 2009, which is incorporated byreference herein in its entirety.

FIELD OF INVENTION

The invention relates to a brake system, especially for a generator, agenerator, especially a direct drive generator, and a wind turbine.

BACKGROUND OF INVENTION

In principle there are two main types of wind turbines in view of thedirect drive configuration of a wind turbine. The first type of a windturbine is the more classical type of a wind turbine comprising agearbox arranged between a main shaft and a generator of the windturbine. The second type of a wind turbine is a gearless type, where thegearbox and the conventional generator are substituted by a multipolargenerator, a so called direct drive or directly driven generator. Such adirect drive generator can be made as a synchronous generator withwinded rotor or with permanent magnets attached to the rotor, or it canbe designed as an alternative type of a generator. One of the challengeswith the direct drive generator is the mechanical brake system. Thebrake system needs to be located at the slowing rotating axis as no gearbox is used. The brake system needs to withstand a large braking momentand large brake discs and callipers are necessary.

The US 2005/230979 describes a wind turbine which minimizes the size ofthe nacelle while providing adequate accessibility to components duringmaintenance operations. The wind turbine comprises: a nacelle and ablade rotor hub adjacent to said nacelle and a main shaft coupled tosaid hub and said nacelle. The generator is coupled to said shaftbetween said nacelle and said hub, wherein said generator includesgenerator rotor adjacent to said shaft, a stator positioned adjacent toand radially outward from said generator rotor; and a brake coupled tosaid generator and said shaft where the brake is positioned radiallyinward from said stator. The invention describes a solution thatminimizes the brake system as the system can be more or less integratedinto the generator. However, the proposed solution minimizes the size ofthe construction and also restricts the size of the brake system whichis unwanted for a direct drive wind turbine where the size of thecallipers and the brake disc should be as big as possible in order towithstand the high braking moments due to the slow rotational speed ofthe rotor. The brake system shown in US 2005/230979 also preventspassage though the generator and it is not possible to go into the hubfrom the nacelle/generator. Furthermore, the invention relates to agenerator with an inner rotor configuration and it not possible to usethe configuration for brake system with outer rotor configuration.

In US 2009/0026771 A1 a wind turbine comprising an electrical generatorthat includes a rotor assembly is disclosed. The wind turbine includes africtional braking system for slowing, stopping or keeping stopped therotation of the wind rotor and rotor assembly. In one implementation,the wind turbine/generator set includes a generator that includes astator assembly and a rotor assembly rotatable about a rotational axis.The rotor assembly includes an active portion and an active portionsupport supporting the active portion. The wind turbine/generator setfurther includes a wind rotor coupled to the rotor assembly, a generatorsupport fixedly supporting the stator assembly and rotatable supportingthe rotor assembly. Furthermore, the wind turbine/generator set includesat least braking device fixed relative to the generator support. Thebraking device includes at least one frictional member operativelyconfigured for frictionally engaging at least a portion of the activeportion support. The rotor assembly is generally located radially inwardof the stator assembly.

SUMMARY OF INVENTION

It is a first objective of the present invention to provide anadvantageous brake system. It is a second objective of the presentinvention to provide an advantageous generator and it is a thirdobjective of the present invention to provide an advantageous windturbine.

The objectives are solved by a brake system, generator, and wind turbineas claimed in the independent claims. The dependent claims definefurther developments of the invention.

The inventive brake system comprises a rotor assembly, a stator assemblyand a rotation axis. The rotor assembly comprises an outer portion whichis located radially outward of the stator assembly. The outer portioncomprises a brake disc. The stator assembly comprises at least onefrictional member. The frictional member is operatively configured forfrictionally engaging at least a portion of the brake disc. Theinventive brake system may especially be used for a generator.

The inventive brake system has the advantage, that the brake disc can bemounted on a cylindrical support structure of an outer rotor. In thiscase the possible large diameter of the machine can be fully used inorder to use a brake disc with largest possible diameter. This increasesthe efficiency of the brake. Moreover, a bigger brake disc and biggerbrake callipers can be used which provides a larger effective contactsurface. A large effective contact surface is necessary in order tomaintain the rotor in a parking position, for example. A furtheradvantage is that more heat can be absorbed and distributed in a largebrake disc compared with smaller brake discs.

Generally, the inventive brake system can be part of a direct drivegenerator or it can be connected to a direct drive generator. Thegenerator may have an outer rotor configuration.

Advantageously the brake disc extends radially inward from the outerportion of the rotor assembly to the rotation axis. In this case theinventive brake system can be used for a direct drive generator.Furthermore, the inventive brake system may be part of a direct drivewind turbine with an outer rotor configuration.

Moreover, the rotor assembly may comprise a flange. The brake disc maybe fastened to the flange. For example, the flange may comprise a numberof holes, preferably bolt holes. The holes may be radially spaced.Preferably the brake disc is fastened to the flange by bolts or screws.

The brake system may be part of a wind turbine with a hub. In this casethe brake system, especially the rotor assembly of the brake system, maycomprise a near end which faces the hub and a far end which is locatedopposite to the hub. Preferably the flange, to which the brake disc isfastened, may be located at the fast end of the rotor assembly, whichmeans opposite of the hub.

The inventive brake system may comprise a rotor support. In this casethe brake disc may be fastened to a flange of the rotor support, forexample by bolts or screws.

The stator assembly may comprise a stationary shaft. The at least onefrictional member may be connected to the stationary shaft. The statorassembly may comprise a bed frame of a wind turbine. The at least onefrictional member may be connected to the bed frame of the wind turbine.The stator assembly may comprise a stator support structure. The atleast one frictional member may be connected to the stator supportstructure. For example, the at least one frictional member, for exampleat least one brake calliper, may be directly mounted to the stationaryshaft or the bed frame of a wind turbine or a stator support structure.

Preferably the at least one frictional member may extend radiallyoutward regarding the rotation axis. For example, the at least onefrictional member may extend radially outward from the stator supportstructure or from the stationary shaft or from the bed frame of a windturbine.

Especially, the frictional member may comprise at least one brakecalliper. Preferably the frictional member comprises at least one brakecalliper on each side of the brake disc, preferably in order to enclosethe brake disc. Advantageously the at least one frictional membercomprises at least one brake calliper system. The at least one callipersystem may comprise at least to brake callipers located on each side ofthe brake disc opposite to each other. For example, the brake callipersystem may comprise at least one calliper bracket. The calliper bracketmay be used for mounting the callipers and/or the brake calliper systemto another component of the brake system, for example for mounting tothe stationary shaft. Each brake calliper system may be connected to acalliper bracket.

Advantageously the brake calliper system may be designed such that it isaligned to the brake disc in axial direction in such a way that nobending moment, especially no axial bending moment, is experienced at afixation point of the brake calliper system. For example, the brakecalliper system may be aligned to the brake disc in axial direction orit may be configured in such a way that no bending moment orsubstantially no bending moment is experienced at a fixation point ofthe brake calliper system to the calliper brackets.

Moreover, the inventive brake system may comprise a rotor lock system.Preferably, the rotor lock system is integrated in the brake system.Preferably, the rotor lock system comprises an automatic actuator. Forexample, the rotor lock system may comprise an interlock, a snap-inlock, a block, an arrest or a barricade, preferably a number of theafore mentioned components.

The rotor lock system can be realised such that the brake disc comprisesa number of recesses, preferably in the inner surface of the brake disc,for example radially and/or symmetrically spaced. The stator assemblymay comprise at least one piston, preferably a number of pistons.Preferably, the piston/pistons is/are located such that it/they areprepared to engage with the recess/recesses. For example, the pistons orthe piston are/is prepared to engage with the corresponding recesses inthe brake disc in order to lock the rotor in a parking position.

Preferably, the lock system may comprise an automatic actuator. Theautomatic actuator can advantageously be configured for pushing thepistons or the piston into the corresponding recesses. The actuator maycomprise hydraulic or electrical means, for example a hydrauliccylinder. In this case the pistons can be pushed into the correspondingrecesses of the brake disc by hydraulic or electrical means. This way,it is possible to lock the rotor in an automated manner.

Furthermore, the brake disc may comprise a number of radial segments. Ifthe brake disc is divided into radial segments it is possible toexchange a large brake disc in an easy way.

The inventive generator comprises an inventive brake system aspreviously described. The inventive generator has the same advantages asthe inventive brake system.

Generally, the generator may have an air gap, which is located betweenstator elements and rotor elements of the generator. The rotor elementscontain permanent magnets for example, while the stator elements containstacked laminate plates, which support at least one winding of thestator coil.

The air gap should be relatively small to ensure a high efficiency ofthe generator. Thus the air gap should stay in a range of only a fewmillimeters. For generators, like direct drive or directly drivengenerators, this is very difficult due to their size. Direct drivegenerators show a diameter of several meters.

Rotor elements and stator elements are typically arranged opposite toeach other, thus the air gap has to ensure that they do not come intocontact while the generator is at operation. Thus the air gap should bevery small to ensure the efficiency of the generator on the one handwhile a certain width of the air gap is needed to prevent mechanicaldamages.

Especially for a direct drive generator it is difficult to keep the airgap in a range of only a few millimeters. This requires therefore veryrigid, massive and heavy support structures for the stator elements andfor the rotor elements.

The air gap of a generator can be determined by tolerances of thepermanent magnets, which are part of the rotor, by tolerances of thestacked laminate-plates, which are part of the stator, and/or bytolerances of the coil-windings, which are part of the stator-coil. Alsoother elements of the generator contribute to the dimensions of the airgap. The air gap may be designed in a way that the elements of the rotorand of the stator do not get in contact, while the rotor rotates aroundits dedicated rotational axis.

The inventive generator may comprise a rotor and a stator.Advantageously, the distance in radial direction (radial distance)between the brake disc and the frictional member is less than thedistance in radial direction (radial distance) between the rotor and thestator. The frictional member can be the brake calliper or the brakecalliper system or part of the brake calliper system, for instance abracket. For example, the radial distance between the brake disc and thefrictional member can be between 1 mm and 5 mm, preferably between 2 mmand 4 mm. The radial distance between the rotor and the stator can bebetween 4 mm and 10 mm, preferably between 5 mm and 7 mm.

If the radial distance between the brake disc and the frictional memberis less than the radial distance between the rotor and the stator, thebrake disc would hit the frictional member, for example the bracket ofthe brake calliper system, before the stator hits the rotor. Thisprevents damages to the generator and increases the safety of thesystem. The radial distance between rotor and stator is also called airgap. The generator may be part of a direct drive wind turbine with aunilateral bearing. The generator may comprises an unsupported end,which is the opposite end of where the bearing is located. By means ofthe inventive generator the air gap at the unsupported end can bemaintained within the narrow tolerances.

The inventive wind turbine comprises an inventive brake system and/or aninventive generator as previously described. The inventive wind turbinehas the same advantageous as the inventive brake system and/or aninventive generator. Preferably the inventive wind turbine may be adirect drive wind turbine. Moreover, the inventive wind turbine maycomprise an outer rotor configuration.

The inventive wind turbine may comprise a nacelle, a hub and agenerator. The generator may be located inside the nacelle or betweenthe nacelle and the hub. The brake system may be connected to thegenerator and/or to the hub. For example, the brake system may be anintegrated part of the generator and/or an integrated part of the hub.

The generator may comprises a near side facing the hub and a far sideopposite to the hub. Preferably the brake system and/or the lock systemmay be located at the far side opposite to the hub.

Since the inventive brake system may be more or less an integrated partof the generator it does not take up extra space inside the nacelle.Moreover, entrance through the generator, especially through the stator,is possible, which is a great advantage. This provides easy access tothe hub. Moreover, easy access to the parts of the brake system,especially if the brake system is located at the far side of thegenerator opposite to the hub, is provided. This allows for easiermaintenance and service.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, properties and advantageous of the present inventionwill become clear from the following description of an embodiment inconjunction with the accompanying drawings. All features areadvantageous alone or in combination with each other.

FIG. 1 schematically shows a wind turbine.

FIG. 2 schematically shows part of an inventive generator with aninventive brake system in a sectional view.

FIG. 3 schematically shows a front view of an inventive brake system.

FIG. 4 schematically shows part of the inventive brake system in asectional view along IV-IV of FIG. 3.

FIG. 5 schematically shows part of the rotor lock system of theinventive brake system in a sectional view along V-V.

FIG. 6 schematically shows the rotor lock system of FIG. 5 in a lockedposition.

FIG. 7 schematically shows part of an inventive wind turbine.

DETAILED DESCRIPTION OF INVENTION

An embodiment of the present invention will now be described withreference to FIGS. 1 to 7. FIG. 1 schematically shows a wind turbine 1.The wind turbine 1 comprises a tower 2, a nacelle 3 and a hub 4. Thenacelle 3 is located on top of the tower 2. The hub 4 comprises a numberof wind turbine blades 5. The hub 4 is mounted to the nacelle 3.Moreover, the hub 4 is pivot-mounted such that it is able to rotateabout a rotation axis 9. A generator 6 is located inside the nacelle 3.The wind turbine 1 is a direct drive wind turbine. The generator 6comprises a near side 19 facing the hub 4 and a far side 20 opposite tothe hub 4.

FIG. 2 schematically shows part of a generator 6 with an outer rotorconfiguration in a sectional view. The generator 6 comprises a statorassembly 7 and a rotor assembly 8. The stator assembly 7 comprises astationary shaft 10 which is located close to the rotation axis 9. Therotor assembly 8 comprises an outer rotor portion 11 which is locatedradially outward of the stator assembly 7. The rotor assembly 8 furthercomprises a brake disc 12. The brake disc 12 may be part of the outerrotor portion 11 or it may be connected to the outer rotor portion 11.The brake disc 12 extends radially inward from the outer portion 11 tothe rotation axis 9. The outer portion 11 of the rotor assembly 8 andthe brake disc 12 are pivot-mounted about the rotation axis 9.

The stator assembly 7 further comprises a frictional member, in thepresent embodiment a brake calliper system 13. The brake calliper system13 is operatively configured for frictionally engaging at least aportion of the brake disc 12. The brake calliper system 13 extendsradially outward from the stationary shaft 10 to the brake disc 12. Thebrake calliper system 13 comprises at least one brake calliper on eachside of the brake disc 12 in order to enclose the brake disc 12.

The radial distance 22 between the brake disc 12 and the brake callipersystem 13 is less than the radial distance 23 (air gap) between theouter rotor portion 11 and the stator assembly 7. Advantageously, radialdistance 22 is between 1 mm and 5 mm, preferably between 2 mm and 4 mm.Preferably, the air gap 23 has a width between 4 mm and 10 mm,advantageously between 5 mm and 7 mm.

FIG. 3 schematically shows a front view of the inventive brake system ofthe generator 6. Elements which correspond to elements of the previouslydescribed Figures are designated with the same reference numerals andwill not be described again in detail. The brake disc 12 comprises aninner surface 21. The inner surface 21 of the brake disc 12 comprises anumber of recesses 15. Preferably the recesses 15 are radially and/orsymmetrically spaced in the inner surface 21.

Generally, the brake disc 12 can be divided into radial segments 12 a,12 b and 12 c. The brake disc 12 can also be divided into any othernumber of radial segments. This makes it possible to exchange a largebrake disc 12 easily.

The brake system further comprises a number of central mounted flanges14, in the present embodiment three central mounted flanges 14. Theflanges 14 are mounted to the stationary shaft 10. The flanges 14 arestaggered about an angle of 120° regarding the circumference of thestationary shaft 10. Alternatively any other number of the flanges 14 ispossible. Preferably the flanges 14 are arranged around thecircumference of the stationary shaft 10 such that adjacent flanges havean equal distance to each other.

The brake system comprises at least one rotor lock system 17. The rotorlock system 17 comprises at least one piston 16. The piston is locatedinside the flange 14 or is located inside of a lock casing. The lockcasing can be connected to the flange 14. Alternatively, the brakesystem can comprise separate flanges for housing the pistons or forbeing connected with at least one lock casing of the rotor lock system17 and separate flanges 14 being connected with the brake system,especially the brake calliper system 13.

The pistons 16 are located such that they are prepared to engage withthe recesses 15 in the inner surface 21 of the brake disc 12.Preferably, the rotor lock system 17 comprises an automatic actuator.The automatic actuator may be configured for actuating the rotor lock.Especially, the rotor lock system 17 may comprise an automatic actuatorfor pushing the pistons 16 into the corresponding recesses 15.Preferably the actuator comprises hydraulic or electrical means, forinstance a hydraulic cylinder. Instead of recesses also holes can bepresent in the brake disc 12 and instead of pistons also pins may beused.

Instead of the described rotor lock system 17 comprising a number ofpistons 16 also a lock system comprising an interlock, a snap-in lock, ablock, an arrest, a barricade or a similar means may be used.

FIG. 4 schematically shows part of the inventive brake system in asectional view along IV-IV of FIG. 3. In FIG. 4 two brake callipers 13Aand 13B are located each on one side of the brake disc 12 opposite toeach other. The two brake callipers 13A and 13B are connected to thecentral mounted flange 14. The flange 14 is connected to the stationaryshaft 10. In FIG. 4 the brake disc is integrated part of the outer rotorportion 11. Alternatively, the brake disc 12 may be a separate elementwhich is mounted to the outer rotor portion 11. For example, the brakedisc 12 can be fastened to a flange of a rotor support, for instance bybolts or screws.

The actuation force for actuating the brake callipers 13A and 13B isdesignated by an error 18. When the brake callipers 13A and 13B areactuated, they frictionally engage a portion of the brake disc 12.

The wind turbine 1 may comprise a bed frame or a support structure ofthe stator. In this case the brake calliper system 13 can be mounteddirectly to the bed frame of the wind turbine 1 or to the supportstructure of the stator.

FIGS. 5 and 6 schematically show part of the inventive brake system in asectional view along V-V of FIG. 3. In the present embodiment the rotorlock system 17 is integrated into the brake system. FIG. 5 schematicallyshows the rotor lock system in an unlocked state. FIG. 6 shows the rotorlock system in a locked state. In FIG. 5 the piston 16 is completelylocated inside of the flange 14 or inside of another component of therotor lock system 17, for example a lock casing. In FIG. 6 the piston 16is pushed into a corresponding recess 15 of the brake disc 12. In thisposition the rotor is locked in a parking position. The piston 16 can bepushed into the corresponding recess 15 of the brake disc 12 byhydraulic or electrical means.

Preferably the inventive brake system is located at the far side 20 ofthe generator 6 opposite to the hub 4. This allows for an easy access tothe brake system and the integrated rotor lock system, especially formaintenance and service. Alternatively, the inventive brake system maybe located at the hub. For example, the inventive brake system maydirectly be connected to the hub.

FIG. 7 schematically shows part of an inventive wind turbine 301. Itcomprises a typical and well known “one-bearing” arrangement. A windturbine 301 comprises a direct drive generator 302, which is arranged onthe upwind side of a tower 303 of the wind turbine 301.

A tower flange 304 is arranged on the top of the tower 303. A bedplate305 is attached to the tower flange 304. The wind turbine 401 comprisesa yaw system—not shown here—which is used to turn the bedplate 305 ofthe wind turbine 301 around the axis 300.

The wind turbine 301 comprises a stationary shaft 306, while the shaft306 has a centre axis 200. The rear side of the stationary shaft 306 isattached to a retaining arrangement 307. On the front side of thestationary shaft 306 a stator arrangement 308 of the direct drivegenerator 302 is arranged. The stator arrangement 308 comprises a statorsupport structure 309 and a lamination stack 310. The lamination stack310 supports windings 311.

The stator support structure 309 comprises two support elements 312 fora two side support of the lamination stack 310. The support elements 312are ring-shaped. They are attached to the outside of the stationaryshaft 306. A hollow cylindrical support element 313 is attached to theouter ends of the ring-shaped support elements 312. The hollowcylindrical support element 313 carries the ring-shaped lamination stack310 and the windings 311.

A rotor arrangement 314 is arranged around the stator arrangement 308.The rotor arrangement 314 comprises a front endplate 315 and a cylinderelement 317. The front endplate 315 is ring-shaped, while the cylinderelement 317 is hollow.

The cylinder element 317 comprises a plurality of permanent magnets 318,which are mounted on the inside of the hollow cylinder element 317. Thepermanent magnets 318 are arranged opposite to the lamination stack 310and the supported windings. An air gap 319 with a width of approximately6 mm is located between the permanent magnets 318 and the laminationstack 310. Preferably, the air gap 319 has a width between 4 mm and 10mm, advantageously between 5 mm and 7 mm. A brake disc 12 is connectedto the cylinder element 317 of the rotor. A brake calliper system 13 isconnected to the stationary shaft 306. The radial distance 22 betweenthe brake calliper system 13 and the brake disc 12 is less than the airgap 319. Advantageously, radial distance 22 is between 1 mm and 5 mm,preferably between 2 mm and 4 mm.

The front endplate 315 is arranged on the stationary shaft 306 via abearing 320. The bearing 320 is capable to transform axial loads in bothdirections of the centre axis A. An appropriate bearing is disclosed inDE 201 16 649 U1 for example.

The stationary part 321 of the bearing 320 is attached to the stationaryshaft 306. The rotating part 322 of the bearing 320 is connected to amounting ring 323. The front endplate 315 as well as the hub 324 areattached to the mounting ring 323. The hub 324 comprises mountingdevices 325 for wind turbine rotor blades—not shown here.

The air gap 319 shown here is uniform to achieve a constant distancebetween the elements of the rotor and the elements of the stator. Theone bearing design is very attractive due to its easy design.

1.-16. (canceled)
 17. A brake system, comprising: a stator assemblycomprises a frictional member; a rotor assembly which comprises an outerportion located radially outward of the stator assembly, the outerportion comprises a brake disc; and a rotation axis, wherein thefrictional member is operatively configured for frictionally engaging atleast a portion of the brake disc.
 18. The brake system as claimed inclaim 17, wherein the brake disc extends radially inward from the outerportion of the rotor assembly to the rotation axis.
 19. The brake systemas claimed in claim 17, wherein the rotor assembly comprises a flangeand the brake disc is fastened to the flange.
 20. The brake system asclaimed in claim 17, wherein the stator assembly comprises a stationaryshaft and the frictional member is connected to the stationary shaft.21. The brake system as claimed in claim 17, wherein the stator assemblycomprises a bed frame of a wind turbine and frictional member isconnected to the bed frame.
 22. The brake system as claimed in claim 17,wherein the stator assembly comprises a stator support structure and thefrictional member is connected to the stator support structure.
 23. Thebrake system as claimed in claim 17, wherein the frictional memberextends radially outward regarding the rotation axis.
 24. The brakesystem as claimed in claim 18, wherein the frictional member comprises abrake calliper.
 25. The brake system as claimed in claim 17, wherein thefrictional member comprises a brake calliper system, which comprises aplurality of brake callipers located on each side of the brake discopposite to each other.
 26. The brake system as claimed in claim 25,wherein the brake calliper system is aligned to the brake disc in axialdirection so that no bending moment is experienced at a fixation pointof the brake calliper system.
 27. The brake system as claimed in claim17, wherein the brake system comprises a rotor lock system.
 28. Thebrake system as claimed in claim 27, wherein the brake disc comprises aplurality of recesses and wherein the stator assembly comprises a pistonfor engaging with one of the plurality of recesses.
 29. The brake systemas claimed in claim 28, wherein the lock system comprises an automaticactuator for pushing the piston into one of the plurality of recesses.30. The brake system as claimed in claim 17, wherein the brake disccomprises a plurality of radial segments.
 31. A generator, comprising: abrake system, comprising: a stator assembly comprises a frictionalmember; a rotor assembly which comprises an outer portion locatedradially outward of the stator assembly, the outer portion comprises abrake disc; and a rotation axis, wherein the frictional member isoperatively configured for frictionally engaging at least a portion ofthe brake disc.
 32. The generator as claimed in claim 31, wherein the aradial distance between the brake disc and the frictional member is lessthan a radial distance between the rotor assembly and the statorassembly.
 33. A wind turbine comprising a brake system, comprising: astator assembly comprises a frictional member; a rotor assembly whichcomprises an outer portion located radially outward of the statorassembly, the outer portion comprises a brake disc; and a rotation axis,wherein the frictional member is operatively configured for frictionallyengaging at least a portion of the brake disc.
 34. The wind turbine asclaimed in claim 33, further comprises: a generator and/or a hub and thebrake system is connected to the generator and/or to the hub.